The present invention generally relates to rotating shafts. More particularly, the invention relates to magnetically driven shafts. Yet more particularly, the invention relates to magnetic drive pumps.
Generally, shafts, for example magnetically driven shafts used in magnetic drive pumps, are made of a relatively tough metal such as steel and supported within bushings that have bearing surfaces on which the shafts can rotate and that serve to maintain shaft alignment. The bushing bearing surfaces generally are made out of a relatively softer material such as brass, bronze, impregnated materials, among others. After a certain amount of use, the bearing surfaces of the bushings can become worn due to the wear of the relatively tough shafts on the relatively soft bearing surfaces. As a result, a shaft can easily become misaligned or skewed in the one or more worn bushings, thereby rotating non-concentrically.
In magnetically driven shafts, one end of the shaft includes magnets secured thereto and a further magnetic field is provided on a driver. The driver magnetic field is rotated about the shaft magnets thereby inducing the shaft to rotate. The driver magnetic field usually is provided as magnets mounted on a driving shaft. However, they can also be provided as electromagnets whose field is rotated.
Generally, a protective sealing or containment can or canister is disposed between the shaft magnets and the driver magnetic field to seal the driven shaft from the driving mechanism. Lubricating fluid is then allowed to flow about the driven shaft but isolated from the driving mechanism. However, as the bushings become worn and the shaft becomes misaligned, there is a danger that the shaft magnets will hit an interior wall of the sealing can, in rotating contact, especially if the arrangement is configured with small tolerances. Similarly, if the driver magnetic field is supported on a rotating shaft secured within bushings, these bushings can become worn and the driver magnetic field can begin to rotate not concentrically and begin contacting the containment can. This rotating contact with the containment can can lead to wear on the can and eventually to a breaking or loss of the sealing function. As a result, there is a danger of leakage through the can.